One frequent well servicing technique for oil and gas formation having low permeability is to artificially “stimulate” to increase the permeability of the production zone(s). Generally, these stimulation techniques are referred to as “fracturing.” Fracturing involves pumping pressurized fluids through perforations in a well casing into a production zone in order to break or fracture pores in the production zone into the casing. Fracturing generally involves first using a tool known as a perforating gun to perforate the production zone adjacent the casing. Thereafter, fracturing fluids are pumped under very high pressures of about 5,000–10,000 psi through the perforations into the formation. The high pressure breaks the formation to form a flow channel for hydrocarbon fluids. Proppants are also injected to prevent the formation from collapsing after the high stimulation pressure is released.
During fracturing, isolation tools are needed to isolate the wellhead from the high pressures of fracturing. In the prior art, these fracturing isolation tools generally seal inside the casing or on the bit guide in a manner which can restrict full bore access to the casing. Full bore access is particularly desirable for fracturing techniques which involve fracturing in stages. After fracturing, the fracturing isolation tool is removed. At this point, since the well may be live, it is necessary to maintain control over the well. One prior art approach is to install a bridge plug, which seals inside the casing. These tools are expensive to rent and to use. Another approach is to control the well pressure with a column of mud or water. However, this procedure can damage the formation. Both of the above approaches require a service crew at the well, which is time and resource intensive.